This invention relates to a differential pressure sensor for use at cryogenic temperatures. The sensor includes a capactive signal generator which is insensitive to magnetic fields and which has electrodes exposed to the pressure difference to be measured. The pressure difference changes the mutual distance d of the electrodes and thus changes the capacity C=.epsilon..sub.o .times..epsilon..sub.r .times.(F/d) of the capacitive transmitter (signal generator) in a predetermined pressure/displacement relationship.
The magnetic fields of fusion reactors with a magnetic inclusion of plasmas can be generated, for economic reasons, only by means of superconducting magnets. For this purpose superconducting cables are used which are build as hollow conductors and cooled with supercritical helium. For reasons of operational safety, the pressure drop of the liquid helium must be measured over a predetermined length of the superconductor to ensure that at all times a sufficient cooling is present and thus an undesired transition from the superconducting state into the normal conducting state cannot occur.
In the periodical entitled Review of Scientific Instruments, April 1980, issue No. 51(4), on pages 509 and 510 there is disclosed a helium vapor pressure gauge for a temperature range down to 0.3 K. The device essentially comprises a measuring condenser whose capacity is altered by moving a diaphragm as an auxiliary electrode towards one of two condenser plates as a function of the gas pressure in a helium chamber closed by the diaphragm.
The above-outlined known measuring device is particularly disadvantageous in that it is complex and expensive to construct a chamber with a diaphragm and further, the development of an appropriate electronic system and a testing in strong magnetic fields would be necessary.